I. Field of the Invention
This invention relates to an end effector for an industrial robot and, more specifically, to a robot end effector for handling windshields, and detecting the presence of a spacer clip on the edge of the windshield.
II A. Discussion of the Technology
Bent laminated windshields for automobiles are fabricated in a series of steps. First, pairs of glass sheets or doublets are placed on skeletal frames and passed through a heating furnace where they deform and sag as a pair to conform to a desired concave upward profile. The two sheets are bent as a pair so that their shapes complement each other throughout the entire extent of the glass sheets.
The next step involves inserting a flexible sheet of plasticized interlayer material e.g., a sheet of plasticized polyvinyl acetal resin, between each matched pair of bent glass sheets to form an assembly to be laminated. To avoid sliding of the glass sheets relative to each other prior to further fabrication operations, the assembly is thereafter heated and passed between one or more sets of nipper rolls to squeeze the heated assembly to force out any entrapped air between the layers.
To complete the adhesive bond between the thermal plastic interlayer and the glass sheets, the glass and plastic interlayer assembly is subjected to a final heating and pressing operation. One technique includes subjecting the assembly to heat and pressure while fully immersed in an autoclave. It is the usual practice to manually unload and place the windshield assembly in autoclave tubs in an upended position. The tubs are then transferred to the autoclave. Spacers are used on the upper edge of windshield assemblies to keep them separated while in the autoclave. The usual autoclave treatment utilizes temperatures of about 225.degree. to 300.degree. F. (107.degree. to 149.degree. C.), and simultaneously elevated pressure of approximately 175 to 225 lbs/sq. in. (1.2 to 1.5 megapascals) for a period of about 20 to 45 minutes.
II B. Presently Available Technology
Whereas the loading of the autoclave tub is generally accomplished manually, it would be more cost effective if the loading could be done automatically. The following patents illustrate the use of vacuum cups and platen to transfer articles such as glass sheets.
U.S. Pat. No. 2,049,850 to Lytle et al. discloses equipment designed to transfer glass sheets which are brought to the apparatus in a stacked upright position, to a horizontal position on a conveyor. Vacuum cups are mounted on a pivoting frame to engage and hold the glass sheet. The carriage moves back and forth along a track while the pivoting frame connected thereto pivots from an upright to a horizontal position.
U.S. Pat. No. 3,178,041 to Wheat discloses an apparatus for automatically handling individual glass sheets and properly stacking them for subsequent use. The apparatus has a plurality of spaced vacuum cups attached to an overhead swinging frame. The glass sheets are engaged by the vacuum cups, lifted off the horizontal conveyor, and swung into an upright position on bucks located on either side of the conveyor. The swing of the frame during successive loading passes varies to compensate for the increased thickness of the stack of sheets.
U.S. Pat. Nos. 3,679,076 and 3,774,783 to Miller et al., and U.S. Pat. No. 3,682,329 to Dean disclose apparatuses for receiving glass sheets from a horizontal conveyor and stacking them on edge. Sheets drop off the end of a horizontal conveyor and onto an angled vacuum platen which receives, aligns and moves the sheets to a stacking location where the sheet is unloaded in an upright position. In U.S. Pat. Nos. 3,679,076 and 3,774,783, the loading buck remains in a fixed location as the vacuum platen and conveyor index forward for each successive unloaded glass sheet, while in U.S. Pat. No. 3,682,329, the collector or stacker member moves backward with each sheet that is stacked.
The following patents illustrate the use of vacuum cups on the end of a manipulator.
U.S. Pat. No. 3,598,263 to Ehmke discloses an articulating device capable of handling large glass sheets which must be accurately positioned. Suction devices are placed around an adjustable frame to engage and support the glass sheet. The apparatus is capable of pivoting and rotating the position of the glass sheet to a desired position.
U.S. Pat. No. 4,065,001 to Ohnaka discloses a jointed manipulator with a vacuum cup at the end of the manipulator arm. The arm is capable of moving and pivoting along a various axis.
U.S. Pat. No. 4,299,533 to Ohnaka discloses a jointed manipulator for transferring objects, e.g., from a belt conveyor to a processor. The manipulator is constructed to have only one degree of freedom. The material holder has a series of suction cups to engage and support the object to be moved.
It would be desirable to have an apparatus that could automatically unload windshield assemblies from one conveyor and load them into an autoclave tub while also detecting the presence of a spacer clip on the assembly and signalling an operator if the spacer clip is missing.